Currently, there are a variety of magnetic stirrers used for suspending biological cells, or tissue growths, in a liquid growing medium. These stirrers typically include a vessel and a closure having a stirring member, or paddle assembly, consisting of a magnet that spins about a vertical axis upon subjecting the stirring assembly to a rotating magnetic field. Known stirring assemblies also include paddles that are designed to stir the cell culture at relative slow speeds to avoid damaging the cells as they are being mixed into the growing medium.
U.S. Pat. No. 4,512,666 discloses a prior art adjustable-height magnetic stirrer having a suspended magnetic impeller that is vertically adjustable by rotating a threaded sleeve member disposed within a threaded support member. By rotating the threaded sleeve magnetic impeller rises up, or down, depending on the direction of rotation, due to it being restrained by a bearing surface at the end of the threaded sleeve member. However, the paddle, or impeller, is of a fixed pitch and therefore the rotational speed of the impeller must be carefully monitored and controlled so as not to damage the fragile cells being stirred.
Because, the cells, or tissue, to be suspended in a growing medium are quite fragile, there is a need in the art for a paddle assembly that allows for better control of the stirring action conducted within magnetic stirring apparatuses.